KR20160011452A - Method for DC Braking of Permanent Magnet Synchronous Motor Using PWM Inverter - Google Patents

Abstract

A method for DC braking a permanent magnet synchronous motor in which a PWM inverter is idling is disclosed. The PWM inverter performs DC current control when the voltage of the smoothing capacitor is within the preset reference value, and stops the DC current control until the voltage of the smoothing capacitor becomes the upper reference value, until it becomes the lower reference value . If the output current remains the same as the DC reference current for a certain period of time during this process, it is determined that the motor is stopped and the DC braking process is terminated. It is possible to normally stop the motor while avoiding the occurrence of an overvoltage in the smoothing capacitor.

Description

[0001] The present invention relates to a DC braking method for a permanent magnet synchronous motor using a PWM inverter,

The present invention relates to a DC braking method using a PWM inverter, and more particularly, to a method of DC braking a permanent magnet synchronous motor under free-running using a PWM inverter.

Since permanent magnet synchronous motors are more efficient than induction motors, they are in the spotlight in terms of energy saving and are difficult to control compared to induction motors. Various disadvantages of PWM (Pulse Width Modulation) It has been overcome by control techniques.

Referring to FIG. 1, the PWM inverter 10 receives a three-phase AC power, rectifies it, accumulates it in a smoothing capacitor, generates a DC voltage, and uses the DC voltage of the smoothing capacitor to drive the permanent magnet synchronous motor 11 .

It is general that the power flow of the PWM inverter 10 has only one direction. That is, since the rectifying section for converting an AC voltage to a DC voltage is constituted by a diode, the power flow is possible only from the power supply end to the motor.

If an inverter failure or momentary power failure occurs during operation of the electric motor 11, the output of the PWM inverter 10 is cut off and the motor 11 in operation at an arbitrary speed is free-running.

As a method for re-driving the idling motor 11, there is a method of measuring or estimating the speed of the electric motor 11 and operating at a target speed by applying a voltage and a frequency matching the speed, (DC) current is applied to stop the electric motor 11 and then to operate at the target speed. The latter is referred to as DC braking.

In the case of DC braking of the idling motor 11 using the PWM inverter 10, the motor 11 operates as a generator from the moment the PWM control is performed to control the DC current, And is accumulated in a capacitor.

2, although the PWM inverter 10 controls the motor 11 with the DC reference current Idc, ref for DC braking, the output current Iout is in the form as shown in FIG. So that the voltage Vdc of the smoothing capacitor rises.

When the voltage (Vdc) of the smoothing capacitor rises, it may exceed the rated voltage of the power semiconductor device. Therefore, in order to prevent the breakdown of the power semiconductor device due to the overvoltage, the PWM output must be cut off. This means that normal DC braking can not be performed. For this, a separate overhead is required to consume the energy stored in the smoothing capacitor by using a braking resistor.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a motor control apparatus and a method of controlling the DC braking, And the like.

According to an aspect of the present invention, there is provided a DC braking method for a permanent magnet synchronous motor using a PWM inverter, including: performing DC current control with a reference current; If the voltage of the smoothing capacitor is less than the first reference voltage, continuing the DC current control according to the output current or ending the DC braking process; Stopping the DC current control when the voltage of the smoothing capacitor is equal to or greater than the first reference voltage and waiting until the voltage of the smoothing capacitor becomes less than the second reference voltage; And performing the DC current control again when the voltage of the smoothing capacitor becomes less than the second reference voltage.

The PWM inverter may terminate the DC braking process when the voltage of the smoothing capacitor is less than the first reference voltage and the output current maintains the same state as the reference current for a predetermined time.

According to the present invention, when DC braking is performed during idling of a permanent magnet synchronous motor using a PWM inverter, the energy stored in the smoothing capacitor can be appropriately adjusted so that the motor can be normally stopped while avoiding occurrence of an overvoltage.

1 shows an example of a motor drive system using a PWM inverter,
Fig. 2 shows an example of a main waveform when a motor under idling is subjected to DC braking,
3 shows a specific example of the PWM inverter,
4 is a flowchart illustrating a DC braking operation of an idling permanent magnet synchronous motor according to an embodiment of the present invention.
5 is an example showing main waveforms when DC motor braking is performed on an idling motor according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 shows a specific example of the PWM inverter 20 that drives the permanent magnet synchronous motor 11 (hereinafter referred to as an electric motor). The PWM inverter 20 receives and processes the three-phase AC power, .

The PWM inverter 20 includes a rectifying section 21 for converting the AC voltage of the three-phase AC power source into a DC voltage, a smoothing capacitor 22 for smoothing the DC voltage rectified by the rectifying section 21, A current detector 24 for detecting the output current (input current of the motor) of the PWM inverter, a control circuit 23 for controlling the output voltage and frequency of the PWM inverter, (25).

The control unit 25 drives the electric motor 11 by controlling each of the power semiconductor elements of the power circuit unit 23 by PWM (Pulse Width Modulation), and when a situation occurs in which the electric motor 11 idles, Thereby stopping the electric motor 11 in operation.

In particular, the control unit 25 monitors the voltage Vdc of the smoothing capacitor 22 in relation to the DC braking operation.

FIG. 4 shows an embodiment of the DC braking method according to the present invention. FIG. 5 shows the relationship between the motor speed Nrpm, the DC reference current Idc, ref, the actual output current Iout, And the voltage Vdc of the capacitor.

In FIG. 5, each section A means an idling period (a period in which the output of the PWM inverter is blocked), and a period B means a period in which DC braking is performed.

When DC braking is started, the controller 25 transmits a DC reference current to the motor 11 to control the DC current (S111).

The DC current control in step S111 is performed through PWM control, and in each section (section B) in which DC braking is performed, the decreasing slope of the motor speed increases.

If the voltage Vdc of the smoothing capacitor during the DC current control is less than the first reference voltage Vdc, off (S112), the control unit 25 proceeds to step S111 according to the output current Iout Or the DC braking process is terminated (S113).

The first reference voltage Vdc, off refers to a reference value for determining whether to continue the DC current control in step S111.

In step S113, when the time T during which the output current Iout detected through the current detection unit 24 and the reference current Idc and ref remain the same is equal to or greater than the preset constant time Th, The DC braking process is terminated.

However, if the time T during which the output current Iout and the reference current Idc and ref remain the same is less than the preset constant time Th, it is determined that the motor 11 has not yet stopped, The DC reference current control is performed.

That is, in the DC reference current control in step S111, when the voltage Vdc of the smoothing capacitor is less than the first reference voltage Vdc, off (S112) and the output current Iout and the reference current Idc, And is performed when the time duration T of the state is less than the predetermined time Th.

If the voltage Vdc of the smoothing capacitor is higher than the first reference voltage Vdc, off (S112), the DC current control in step S111 is stopped (S114) and the voltage Vdc of the smoothing capacitor 2 reference voltage (Vdc, on) (S115).

Here, the second reference voltage Vdc, on means a reference value for judging whether or not the DC current control is resumed. The first reference voltage Vdc, off, the second reference voltage Vdc, on, '.

When the voltage Vdc of the smoothing capacitor becomes lower than the second reference voltage Vdc, on during the waiting in step S115, the flow advances to step S111 to perform the DC current control again.

Referring to FIG. 5, when the PWM control is performed, the speed of the electric motor 11 decreases faster than when idling, but the voltage Vdc of the smoothing capacitor rises.

That is, the motor speed reduction slope in each section (section B) where the DC reference current Idc, ref is transmitted and DC braking is performed becomes larger than the motor speed reduction slope in the idling section (section A).

In addition, even when DC braking is performed in each section B, the output current Iout has a frequency component corresponding to the rotation of the motor, thereby raising the voltage Vdc of the smoothing capacitor.

If the voltage Vdc of the smoothing capacitor is less than the first reference voltage Vdc, off, there is no risk of destruction of the power semiconductor element due to the overvoltage, so the DC current control is continued.

At this time, it is determined whether the actual output current Iout is equal to the DC reference current Idc, ref to determine whether the electric motor 11 has stopped.

The output current Iout has the same magnitude as the DC reference current Idc and ref because the actual output current Iout has the frequency component corresponding to the rotation of the motor even if the DC current control is performed If it has been continued for the predetermined time Th, it can be determined that the electric motor 11 is stopped, and the DC braking process is terminated.

If the voltage Vdc of the smoothing capacitor is equal to or greater than the first reference voltage Vdc, off, the PWM control is cut off to protect the power semiconductor device, thereby suppressing the voltage Vdc of the smoothing capacitor from rising.

When the voltage (Vdc) of the smoothing capacitor becomes less than the second reference voltage (Vdc, on) while the PWM control is cut off, the DC current control is restarted again.

In this way, until the DC braking process is completed, the sections A and B are alternately performed.

The energy stored in the smoothing capacitor 22 at the time of DC braking is proportional to the speed of the electric motor 11. [ That is, the higher the speed of the electric motor 11, the greater the upward slope with respect to the voltage Vdc of the smoothing capacitor.

It is to be understood that the present invention is not limited to the above-described embodiment, and that various changes and modifications may be made by those skilled in the art without departing from the technical spirit of the present invention. to be.

10, 20: PWM inverter 11: Electric motor
21: rectification part 22: smoothing capacitor
23: power circuit part 24: current detection part
25:

Claims (2)

A DC braking method for a permanent magnet synchronous motor using a PWM inverter,
Performing DC current control with a reference current;
If the voltage of the smoothing capacitor is less than the first reference voltage, continuing the DC current control according to the output current or ending the DC braking process;
If the voltage of the smoothing capacitor is equal to or higher than the first reference voltage, the DC current control is stopped, and the voltage of the smoothing capacitor is decreased until the voltage becomes less than the second reference voltage (first reference voltage> second reference voltage) Waiting; And
And performing the DC current control again when the voltage of the smoothing capacitor becomes less than the second reference voltage. The DC braking method of a permanent magnet synchronous motor using the PWM inverter according to claim 1, The method according to claim 1,
When the voltage of the smoothing capacitor is less than the first reference voltage and the output current maintains the same state as the reference current for a predetermined period of time, the DC braking process is terminated. Otherwise, the DC current control is continued DC Braking Method of Permanent Magnet Synchronous Motor Using PWM Inverter with.

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